1. Field of the Invention
The present invention relates to a hub and, more particularly, to a normally closed soundless ratchet hub assembly for a bicycle.
2. Description of the Related Art
A conventional hub assembly for a bicycle in accordance with the prior art shown in FIGS. 9 and 10 comprises a shaft 53, a hub body 80 rotatably mounted on the shaft 53, a driven ring 82 secured in the hub body 80 to drive the hub body 80 to rotate relative to the shaft 53 and having an inner wall provided with a plurality of oneway ratchet teeth 81, a drive seat 50 rotatably mounted on the shaft 53 and having an end face provided with a plurality of drive blocks 51 each having a surface provided with an oblique driving slot 52, a support ring 54 secured on the drive seat 50 and protruding from the drive blocks 51, a rotation ring 61 mounted on the support ring 54 and having a periphery provided with a plurality of receiving slots 611, a plurality of pawl members 62 each pivotally mounted in a respective one of the receiving slots 611 of the rotation ring 61 to releasably mesh with the oneway ratchet teeth 81 of the driven ring 82 and each having a side provided with a guide post 621 which is movable in the driving slot 52 of a respective one of the drive blocks 51, a mounting sleeve 74 mounted on the shaft 53, a limit ring 70 mounted on the mounting sleeve 74 and attached to the rotation ring 61 to rotate in concert with the rotation ring 61, a damper 73 mounted on the mounting sleeve 74 and pressing the limit ring 70 to damp a rotation movement of the rotation ring 61, and an elastic member 63 mounted on the rotation ring 61 and pressing each of the pawl members 62 to detach each of the pawl members 62 from the oneway ratchet teeth 81 of the driven ring 82 at a normal state.
The drive seat 50 has an outer surface provided with a plurality of axially extending fixing channels 55 for mounting at least one sprocket (not shown). The driving slot 52 of each of the drive blocks 51 has an outer side 522 and an inner side 521. The rotation ring 61 has an inner portion provided with a mounting hole 64 rotatably mounted on the support ring 54. Each of the pawl members 62 has a first end provided with an enlarged pivot shaft 622 pivotally mounted in the respective receiving slot 611 of the rotation ring 61 and a second end provided with a locking detent 623 which is movable with the guide post 621 to mesh with or detach from the oneway ratchet teeth 81 of the driven ring 82. The locking detent 623 of each of the pawl members 62 is in line with the guide post 621. The limit ring 70 has an inner portion provided with a stepped receiving hole 72 mounted on the mounting sleeve 74 to receive the damper 73. The limit ring 70 is located between the support ring 54 and the mounting sleeve 74. The damper 73 is secured in the receiving hole 72 of the limit ring 70 and is located between the limit ring 70 and the mounting sleeve 74. The damper 73 is made of a resilient material and has an inner wall 730 closely fit onto the mounting sleeve 74 and an outer wall 732 pressing the limit ring 70 to provide a damping force to a rotation movement of the limit ring 70. The mounting sleeve 74 is inserted into the drive seat 50 and is located between the drive seat 50 and the hub body 80.
In assembly, the hub body 80 is connected to a wheel (not shown) of the bicycle, the shaft 53 is connected to a frame (not shown) of the bicycle, and the sprocket on the drive seat 50 meshes with and is driven by a chain (not shown) which is driven by a chainwheel (not shown) which is driven by a pedal (not shown) that is pedalled by a rider. Thus, each of the pawl members 62 is initially pressed inward by the elastic member 63 to disengage the oneway ratchet teeth 81 of the driven ring 82, so that the driven ring 82 is released from and non-rotatable with the drive seat 50 at a normal state. At this time, the guide post 621 of each of the pawl members 62 is located at the inner side 521 of the driving slot 52 of the respective drive block 51.
In operation, when the pedal is pedalled by the rider, the chainwheel is driven by the pedal to drive the chain which drives the sprocket of the drive seat 50 so as to rotate the drive seat 50 forward, so that the drive seat 50 is rotated forward relative to the shaft 53, and the drive blocks 51 of the drive seat 50 are also rotated forward relative to the shaft 53. At this time, the damper 73 provides a damping force to the rotation movement of the limit ring 70 so that the rotation ring 61 and the limit ring 70 will not be rotated with the drive blocks 51 of the drive seat 50. In such a manner, when the drive blocks 51 of the drive seat 50 are rotated forward relative to the shaft 53, the guide post 621 of each of the pawl members 62 is moved from the inner side 521 to the outer side 522 of the driving slot 52 of the respective drive block 51, and each of the pawl members 62 is pivoted outwardly relative to the respective receiving slot 611 of the rotation ring 61, so that the locking detent 623 of each of the pawl members 62 is also moved outwardly to mesh with the oneway ratchet teeth 81 of the driven ring 82. Thus, the driven ring 82 is combined with the rotation ring 61 and the drive blocks 51 of the drive seat 50 by the pawl members 62, so that when the drive seat 50 is rotated forward relative to the shaft 53, the driven ring 82 is driven by the drive seat 50 to drive the hub body 80 to rotate forward relative to the shaft 53 so as to move the wheel forward.
On the contrary, when the pedal is pedalled by the rider to move backward, the chainwheel is driven by the pedal to drive the chain which drives the sprocket of the drive seat 50 so as to rotate the drive seat 50 backward relative to the shaft 53, so that the drive seat 50 is rotated backward relative to the shaft 53, and the drive blocks 51 of the drive seat 50 are also rotated backward relative to the shaft 53. At this time, the damper 73 provides a damping force to the rotation movement of the limit ring 70 so that the rotation ring 61 and the limit ring 70 will not be rotated with the drive blocks 51 of the drive seat 50. In such a manner, when the drive blocks 51 of the drive seat 50 are rotated backward relative to the shaft 53, the guide post 621 of each of the pawl members 62 is moved from the outer side 522 to the inner side 521 of the driving slot 52 of the respective drive block 51, and each of the pawl members 62 is pivoted inwardly to retract into the respective receiving slot 611 of the rotation ring 61, so that the locking detent 623 of each of the pawl members 62 is also moved inwardly to disengage the oneway ratchet teeth 81 of the driven ring 82. Thus, the driven ring 82 is released from the rotation ring 61 and the drive blocks 51 of the drive seat 50 by the pawl members 62, so that when the drive seat 50 is rotated backward relative to the shaft 53, the driven ring 82 together with the hub body 80 is not driven by the drive seat 50, and the drive seat 50 idles.
Thus, when the drive seat 50 is rotated backward by the pedal, each of the pawl members 62 is retracted into the respective receiving slot 611 of the rotation ring 61, and the locking detent 623 of each of the pawl members 62 disengages the oneway ratchet teeth 81 of the driven ring 82 constantly, so that each of the pawl members 62 will not touch the driven ring 82 when the pedal is driven backward to prevent from producing a noise when the pedal is driven backward. In addition, each of the pawl members 62 is separated from the driven ring 82 when the pedal is driven backward so that the hub body 80 is separated from the drive seat 50, and a backward rotation of the hub body 80 will not drive the drive seat 50 and the pedal to prevent the pedal from being driven when the hub body 80 is rotated backward.
However, a sliding friction is produced between the guide post 621 of each of the pawl members 62 and the driving slot 52 of the respective drive block 51 during movement of the drive seat 50, so that the drive seat 50 is not operated smoothly and stably. In addition, the damper 73 is made of an annular elastic plate so that the damper 73 has an unevenly distributed tension and easily produces an elastic fatigue.